Non-bitter protein preparations are obtainable by performing a reversed hydrolysis. Proteolytic enzymic reactions are reversible as are other enzymic reactions. A reversal of the enzymic degradation of peptide bonds is termed a plastein reaction, and a protein-like product synthesized by a plastein reaction is termed plastein or plastein material [vide e.g. Horowitz, J. & Haurowitz, F. (1959); Biochim. Biophys. Acta., 33, 231-237; and Determann et al. (1963); Helv. Chim. Acta., 46, 2498]. Plastein material is different from protein and may be regarded as a mixture of high molecular polypeptides. In fact Wieland et al. [Wieland, T; Determann, H. & s Albrecht, E. (1960); Ann., 633, 185 ] define plastein reaction as the formation of high molecular polypeptides.
Various microbial proteases are known to posses plastein synthetic activities. Well known proteases also known for their plastein synthetic activities are pepsin, .alpha.-chymotrypsin, trypsin, and papain [vide e.g. Fujimaki, M.; Kato, H.; Arai, S. & Yamashita, M. (1971); J. Appl. Bact. 34(1), 119-131].
At least four points are hitherto believed to be complied with for the plastein reaction to proceed effectively. First, the concentration of substrate should be high. Second, the substrate should be of low molecular weight. Third, the pH for synthesis of the plastein is different than for hydrolysis of the protein. The pH range for synthesis of plastein is narrower than the pH range for hydrolysis. Fourth, a relatively long incubation time should be applied with.
Apart from removing bitterness of hydrolysates, the plastein reaction has other food processing potentials, e.g. preparing gel-like products with excellent visco-elastic properties for incorporation in different types of foods, preparing products with improved amino acid composition using mixtures of hydrolysates as substrates, preparing products with very high level of a single amino acid which could be used as a dietary supplement to certain foods, and preparing special types of soluble peptides having important flavour or other characteristics.